Conventionally, various stators used in an axial gap electrical rotating machine have been proposed. For example, U.S. Pat. No. 3,159,764 discloses a single-phase armature coil formed by a printed circuit on an insulating member. The armature coil comprises two pairs of half-turn conductors of which inner/outer peripheries are connected together, respectively by a through-hole technique used for a printed circuit board.
JP 51-104501A discloses a stator coil comprising a discoid unit coil having half coils in a predetermined shape formed in a radially on both surfaces of an insulated substrate. According to the unit coil, one-turn coil is formed by connecting end portions of the half coils at both sides protruding at inner/outer peripheries of the insulated substrate. Plural unit coils are stacked together, and the half coils have at least two different lengths so that an end portion of each half coil is located on a different circumference of circle.
JP 04-331431A discloses a structure of a stator coil in which a circuit pattern is printed on a resin substrate to be held, a recess is formed therein, and a stator coil is fitted therein, thus positioning, fixing, and wiring of the stator coil are carried out simultaneously.
JP 2006-288074A discloses a structure of an axial gap electrical rotating machine. The electrical rotating machine has an electromagnetic coil that comprises plural conductive bars, and respective leading ends thereof which are to be conducted one another are joined together. According to this electrical rotating machine, as the electromagnetic coil is formed by the conductive bars, a step of winding up an electromagnetic coil around an iron core can be simplified, thus improving the productivity.
An explanation will be given of an electrical rotating machine disclosed in JP 2008-61357A with reference to FIG. 12. FIG. 12 is a perspective view schematically showing a connection structure of a coil portion of a stator coil used in an axial gap electrical rotating machine. As shown in the figure, a stator coil 100 for an axial gap electrical rotating machine has an annular (ring) coil plate 101, and a coil bus bar (not shown) which is connected to a power feeding system (not shown) arranged at, for example, an inner periphery side of the coil plate 101. The coil plate 101 is formed in such a way that a first coil plate element 101A having a wiring pattern 102 and a second coil plate element 101B having a wiring pattern 103 face with each other so that the wiring pattern 102 and the wiring pattern 103 are oppositely oriented in a circumferential direction, and outer periphery edges and inner periphery edges are joined together with a space 110 so that the facing wiring patterns 102, 103 are spaced apart from each other.
Multiple numbers of polygonal-line coil segments 104a are formed across an entire annular region where the wiring pattern 102 is formed. The polygonal-line coil segments 104a form a coil bundle as a whole. Each polygonal-line coil segment 104a is supported by an outer periphery edge supporting member 151 and an inner periphery edge supporting member 152. A slit 105 is formed between adjoining polygonal-line coil segments 104a. 
The polygonal-line coil segment 104a has a width in a circumferential direction which is wide at the outer periphery side and is narrow at the inner periphery side so as to form the slit 105. The polygonal-line coil segment 104a also has a central straight-line portion 101c arranged at a center, an oblique portion 101b supported by the outer periphery edge supporting member 151 and bent in an oblique direction, and another oblique portions 101d supported by the inner periphery edge supporting member 152 and bent in another oblique direction (see, in more detail, FIG. 13 of JP 2008-61357A). The polygonal-line coil segments 104a further have terminal portions, respectively, formed at a part thereof, and the terminal portions are connected by a bus bar or the like. One terminal is used as a power feeding input terminal 120, while another terminal is used as a power feeding output terminal 121, so that a U-phase coil loop having both coil loop elements connected in series is formed.
Note that FIG. 12 shows the U-phase coil loop only as an example, a V-phase coil loop and a W-phase coil loop have the same shape and the same structure as those of the U-phase coil loop and only wirings differ, so that explanations of those coil loops are omitted to simplify the explanation.